Light after compiling issue

Hello. I’m sorry for this question but i just started to learn about unreal and i’m facing a problem with a simple window.

Before i compile the scene, everything looks all right:

But after compiling this happens:

Increase the lightmap resolution on the object receiving the shadows, the filtering will make shadows look like that when it’s too low (because the pixels are large)

When i set the lightmap resolution higher, the light simply disappear or get worse (128 resolution). But with resolution = 2 for example, it worked. Can you explain it to me?

Are they BSPs? It’s been awhile, but I think BSP lightmap resolution is backwards.

Oh yes, BSP. Ok so haha. Thank you so much, you helped a lot!

With BSP the resolution is the number of physical units per pixel, so the lower the number the higher the detail.